The pentoxylon plant

Abstract

The various dispersed organs belonging to the Pentoxylon plant viz. Pentoxylon (stem), Nipaniophyllum (leaf), Sahnia (male flower) and Carnoconites (female cone) have been studied in detail. Apart from the long shoots (type 1 shoots), the plant bore three different kinds of short shoots: the thick woody short shoots, each with a broadly conical head (type 2 shoots); the slender parenchymatous short shoots (type 3 shoots); and the slightly thicker parenchymatous short shoot (type 4 shoot) terminating in a Sahnia flower. In addition to the well known Nipaniophyllum raoi leaves a second species, N. hobsonii sp. nov., is recognized. In Sahnia the sporangiophores were borne on a collar-like structure formed by the raised margin of the receptacle. The broadly conical head of the thick woody short shoot (type 2 shoot) might be the basis of the cone-bearing branchlets of Carnoconites fruits. The seeds of Carnoconites are spirally arranged rather than being in longitudinal rows as previously suggested. Pentoxylon was probably a shrubby plant that grew beside water. It sent up erect branched leafy shoots that, after a few seasons of growth, flopped onto the ground or on other stems, making a thicket. Although the stem, Pentoxylon, resembles Medullosa and Rhexoxylon anatomically, the reproductive parts of the plant, Sahnia and Carnoconites, are unlike those of any group of gymnosperms. The Pentoxylon plant is accordingly regarded as an extinct gymnosperm of unknown affinity. Nipanioxylon guptai has previously been regarded as related to Pentoxylon, but its holotype is believed to be a conifer and has nothing to do with the Pentoxylon plant.